Method of making hose for low-temperature liquids



June 11, 1968 BOND, JR" ET AL 3,387,449

METHOD OF MAKING HOSE FOR LOW-TEMPERATURE LIQUIDS 2 Sheets-Sheet 1Original Filed Feb. 24, 1960 INVENTORS FRANK D. BOND, JR.

LADISLAS C. MATSCH JAMES A. PROCTOR 1m, F. @3700 A 7' Tom/Er June 11,1968 F. D. BOND, JR, ET AL. 3,387,449

METHOD OF MAKING HOSE FOR LOW-TEMPERATURE LIQUIDS Original Filed Feb.24, 1960 2 Sheets-Sheet 2,

INVENTORS FRANK D. BONDMR. LADISLAS C.MATSCH JAMES A. PROCTOR ATTORNEYUnited States Patent 3,387,449 METHG'D @F MAKENG HGSE FORLUW-TEMEPERATURE LIQUHDS Frank D. Bond, in, Eutialo, Ladieslas C.Matsch, Kenmore, and Flames A. Proctor, 'lionawanda, N.Y., assignors toUnion Carbide Corporation, a corporation of New York Application May 20,1963, Ser. No. 232,834, new Patent No. 3,240,234, dated Mar. 15, 1965,which is a division of application Ser. No. 10,598, Feb. 24, 1960.Divided and this application Aug. fill, 1965, Ser. No. 498,175

6 Claims. (@l. 57-160) This is a divisional application of Ser. No.282,834 filed May 20, 1963, now Patent No. 3,240,234 by F. D. Bond, Jr.,et al., which in turn is a divisional application of Ser. No. 10,598,filed Feb. 24, 1960 by F. D. Bond, Jr., et al., now abandoned.

This invention relates to a method of making flexible hose fortransferring low-boiling liquids at temperatures below about 120 C., andmore particularly to a method of making flexible, insulated hose fortransporting liquid hydrogen, liquid helium and the like.

When low-boiling or cryogenic liquid transfers are conducted betweenvessels, either or both of which are mobile (or portable), theconnection of rigid transfer piping requires accurate orientation ofequipment in three dimensions. Where such equipment is difficult tomove, it would be advantageous to make the connection by a flexiblehose.

Heretofore, liquid oxygen and nitrogen have been transferred fromtransport vessels to stationary storage tanks in flexible uninsulatedhoses of large diameter. Such hoses were adequate for this servicebecause the liquids were relatively inexpensive and because thevolumetric flow rates were high, thus resulting in small percentageevaporation of the total liquid due to heat inleak. However, theexpanding usage of such liquids often far remote from the point ofproduction may greatly increase their value at the point of consumptionand require extreme conservation measures. Furthermore the increasedutilization of more expensive cryogenic fluids boiling below about 196C., as for example liquid hydrogen and liquid helium, has created a needfor flexible transfer hoses which are smaller in size and moreeffectively insulated against heat leak.

A satisfactory flexible hose for such service should possess at leastthe following characteristics:

(1) structurally safe for processing all atmospheric gases and hydrogen.

(2) Capable of restricting heat leakage to a rate compatible with thecost of the refrigerated liquid handled.

(3) Free from cold spots on the jacket which could present a combustionhazard due to air condensation, a handling hazard, or develop frostsuflicient to impede manipulation.

(4) Adequate flexibility and durability at the lowest anticipatedtemperature which is about 4 K., the boiling point of helium atatmospheric pressure.

(5) Minimum cooldown flash-off.

A principal object of the present invention is to provide a method ofassembling a flexible, thermally insulated hose for transporting lowboiling liquids.

Additional objects and advantages of this invention will be apparentfrom the ensuing disclosure and the appended claims.

In the drawings:

FIG. 1 is an elevational view, partly in section, of a flexible hoseembodying the principles of the invention;

FIG. 2 is an isometric view of a composite insulating material employedin the invention and shown in a flattened position with parts brokenaway to expose underlying layers;

3,387,449 Patented dune M, 1968 FIG. 3 is an elevational view, partly insection, of a flexible hose embodying the present invention andincluding an adsorbent-getter space;

FIG. 4 is an isometric view of a cylinder illustrating the first step ofthe present method for applying flexible, composite heat insulatingmaterial to a curved surface;

FIG. 5 is an isometric view of a cylinder illustrating the final step ofthe present method for applying flexible, composite heat insulatingmaterial to a curved surface; and

FIG. 6 is an isometric view of a cylinder illustrating the steps of analternative novel method for applying flexible composite heat insulatingmaterial to a curved surface, according to the present invention.

Briefly, one aspect of the invention comprises a hose for transportinglow-boiling liquids including a flexible corrugated metallic innerconduit, a larger flexible corrugated metallic jacket beingconcentrically spaced around the inner conduit so as to form anevacuable annular insulation space therebetween, the minimum diameter ofthe flexible corrugated jacket being greater than the maximum diameterof the flexible corrugated inner conduit. The annular insulation spaceis substantially filled with a composite insulating material comprisingalternate layers of radiation impervious barriers and low heatconductive fibrous sheets. In a preferred form, the radiation imperviousbarriers are aluminum foil and the low heat conductive layers arepermanently precompacted sheets of unbounded glass fiber paper.

This invention also includes a method for applying alternate layerinsulation in which at least one component of the insulation is providedin strip form and helically wound around a curved surface, the edges ofthe spirals being overlapped to provide a con inuous discrete layer ofthe first component between two continuous discrete layers of a secondcomponent.

A corrugated tube is essentially a bellows, and it is well-known thatwhen such tubes are exposed to a substantial pressure differential, theywill expand or contract as a spring. Furthermore, the forces exerted bysuch corrugated tubes are considerable even at such low pressuredifferentials as 15 psi. This force can be calculated by multiplying thepressure differential times the average cross-sectional area exposed tothe P. Thus, a 3-inch corrugated tube when evacuated can exert acontracting force of almost lbs. imposing internal pressure on acorrugated tube will cause elongation with a force of similar magnitude.

Based on the foregoing considerations it would logically appear to oneskilled in the art that assembling two such tubes together in concentricfashion and evacuating the space there/between would cause the outercorrugated jacket to contract and the inner corrugated conduit to buckleseverely. If a substantial positive pressure con siderably aboveatmospheric is now improved by fluid inside the inner corrugatedconduit, it will tend to elongate but being restrained by the outercorrugated jacket, the forces tending to cause buckling will be evenfurther increased. Thus, the entire assembly would appear to be highlyunstable and not at all suitable for a vacuuminsulated structure inwhich the inner and outer walls must not be permitted to touch eachother.

Another critical factor to be considered is the extreme compressionsensitivity of the alternate layer type of insulation. That is, as thelayers are compressed closer and closer together, the solid conductancein the direction perpendicular to layers, increases appreciably. Theabovementioned buckling tendency of the inner conduit would appear toimpose severe localized compression on the alternate layer typeinsulation if the latter is to be employed as a separator and supportfor the concentric corrugated members. Logically, this would cause areasof high heat conductance at the localized points of compression.

In spite of these enumerated problems, it has been unexpectedly foundthat the particular combination of elements constituting the presentinvention provides an improved flexible hose for transportinglow-boiling liquids which restricts heat inleak to a very small value,and which retains adequate flexibility and durability at the lowestansicipated temperature of 4 K.

Referring now more specifically to the drawings and particularly toFIGS. 1 and 2, the present flexible hose includes corrugated innerconduit for transporting the low temperature liquid, and corrugatedouter jacket Jill arranged concentrically with an annular space 12therebetween. The annular space between the two tubes is filled withcomposite insulation 13, and maintained under a vacuum pressure of belowabout microns of mercury.

The corrugated inner conduit 10 and outer jacket 11 may if desired, beexternally covered with wire braid 14. Where the low temperature liquidsupply pressure is low, the inner conduit braid may be eliminated, thusreducing liquid flash-off during cool-down of the hose. The advantage inusing wire braid on the inner conduit 10 is that the allowable workingpressure of the hose may be increased. The elimination of such wirebraid is particularly feasible in small diameter hoses. This wasdemonstrated by tests in which a 1-inch diameter flexible tube withoutbraid was hydraulically pressurized to 250 p.s.i.g. Deformation of thehose was found to be linear up to 200 p.s.i.g.; ie the elastic limit ofthe hose was not exceeded below this pressure. At 250 p.s.i.g., apermanent elongation of 1.6% resulted. Larger diameter corrugated tubesof commercially available thicknesses benefit more by external wirebraid because they cannot withstand as much pressure without exceedingthe elastic limit.

Stainless steel is the preferred material for the flexible, corrugatedmetal tubes because of its higher strength and welding convenience.Higher strength results in less mass of metal in contact with the liquidand requires less refrigeration to cool the hose to operatingtemperature. As to welding, the end connections on flexible hoses forcryogenic service are preferably constructed of low-conductive stainlesssteel, and the use of other metals such as bronze for the corrugatedhose would require a dissimilar metal joint between the tube and the endconnection. Dissimilar metal joints are less dependable in high-vacuumservice than homogeneous welds between similiar metals.

The corrugated tubing is preferably the seamless type to minimize thepossibility of vacuum leaks which in turn would decrease the insulationefiiciency. However, welded corrugated tubing has been foundsatisfactory for use in the present invention, but a mass spectrometric(helium) leak test should be conducted on the tubes before assembly ofthe hose.

Corrugated flexible tubing is normally available in two forms: In theannular type illustrated in FIG. 1, the corrugations are separate andare formed normal to the tube axis, while in the helical type of FIG. 3the corrugations are pitched and continue in helical form along thelength of the tube. Hoses formed with helical convolutions appear tooffer 75% as much flow resistance as those formed with annularconvolutions. For this reason, the former are preferred in the practiceof this invention.

Highly efficient insulation is important in flexible cryogenic hosesbecause it avoids unnecessary loss of valuable low-temperature liquids.Uniformity of insulation is also important in order to avoid localizedcold spots on the hose. Cold spots not only result in increased heatinleak, but may also cause severe burns to operators handling or comingin contact with the hose. Furthermore, air may condense on a cold spot,thus producing a liquid enriched in oxygen which may be hazardous incontact with inflammable materials. High insulating efficiency coupledwith low density and low heat capacitance are also important incryogenic hoses in order to minimize the loss of expensive refrigerationneeded to cool the hose repetitively to operating temperature. Theseinsulating requirements must be met while preserving flexibility andthinness of the insulating layer.

The present alternate layer insulation provides unexpected advantages invacuum-insulated flexible hoses. As more fully described and claimed incopending US. Ser. Nos. 597,947, 824,690 and 4,298, filed respectivelyon July 16, 1956, July 2, 1959 and Ian. 25, 1960, in the name of L. C.Matsch, now US. Patents 3,007,596, 3,009,600 and 3,009,601,respectively, the low conductive component is a fibrous insulation 15which can be produced in sheet form. Examples of the latter include afilamentary glass material such as glass wool and fiber glass,preferably having fiber diameters of less than about 50 microns. Alsosuch fibrous materials preferably have a fiber orientation substantiallyperpendicular to the direction of heat flow across the insulation. Asatisfactory material consists of an elastic flutfy "web of unbondedfibers having individual fiber diameters of 0.2 to 5 microns and woundwith sufficient compression to provide between 5 and 50 layers per inchthickness. Best results are obtained when the assembled low-conductivefibrous layers are permanently precompacted in an unbonded paper formhaving a density of less than 8 grams per sq. ft. as distinguished fromelastically compressed, web forms and have individual fiber diameters ofless than about 5 microns and preferably between .05 and 1.0 microns.For best results from the standpoints of insulating elficiency and easeof assembly, the fibrous paper is provided in densities of less than 3grams per sq. ft. Also, such fibers are preferably less than about 0.5inches long, and installed with the radiation-impervious layers so as toprovide a composite insulation under a compressive load of less than0.03 lbs. per sq. in.

The spaced radiation-impervious barriers lie of the composite, alternatelayer insulation may comprise either a metal, metal oxide or metalcoated material such as aluminum coated plastic film, or other radiationreflective or radiation adsorptive material, or a suitable combinationthereof. Radiation reflective materials comprising thin metal foils areparticularly suited in the practice of the present invention, and inparticular, reflective sheets of foil, e.g. aluminum, having anuninstalled emissivity of between about 0.005 and 0.2, and a thicknessbetween about 0.2 millimeters and 0.002 millimeters. Aluminum foilshaving a thickness between about 0.005 millimeters and 0.02 millimetershave been found to give best results. Also, the composite insulation ispreferably applied so as to provide between about 40 and 250 radiantheat reflecting shields per inch of insulation space cross-section.

The heat leak for small size hoses up to and including 1 /2" insidediameter constructed in accordance with this invention and employingaluminum foil-permanently pro-compacted glass fiber alternate layerinsulation has been found to be between about A and /5. B.t.n. perft.-hr. when the insulation jacket pressure is about 0.1 microns. Thisis substantially lower than the corresponding heat leak for any knownprior art flexible conduits for lowtemperature liquids. For example, inone such conduit employing straight vacuum insulation without any typeof filter, rediation alone contributes at least 1 Btu. per linear ft.per hr. heat inleak. Uther radiation reflective materials which aresusceptible of use in the practice of the invention include tin, silver,gold, copper, cadmium or other metals. When fiber sh ets are used as thelowconductive material, they may additionally serve as a support meansfor relatively fragile radiation impervious sheets.

As previously mentioned, it has been found that the present alternatelayer insulation provides special advantages in vacuum-insulated hoses,particularly the metal foil-fibrous sheet combination. The pressureimposed by the metal foils prevents fibers from dropping into theconvolutions of the metal tubes. Loose fibers or other par ticulatematerial between the corrugations should be avoided because they wouldabrade the metal, prevent free flexing of the hose, and may overstrainthe corruga tions on the inner radius of a bend. Hoses insulated withpowderous materials would be especially susceptible to damage andimproper performance for these reasons.

Another unique advantage of the combination metal foil and fiberinsulation in the present hose is that the foils serve to protect therather fragile fiber sheets against damage due to hose flexure. Withoutfoils the severe abrasion and compression imposed repeatedly on thefibrous insulation by the rough, uneven metal surfaces will soon breakand separate the brittle unbonded fibers. Bare uninsulated areaseventually develop through which the inner conduit and jacket makemetal-to-metal contact with consequent high heat transmission. Thereflective foils absorb the abrasion, distribute the compressive loadsmore uniformly through the insulation, and hold the unbonded fibersevenly distributed in the respective layers.

Still another important advantage of using alternate layer insulation inthe present hose is that such insulation provides an excellentcontinuous spacer to maintain the concentricity of the liquid conduitwithin its vacuum jacket. No additional spacers or tube separators withtheir attendant heat leak, are required. In previous attempts to providesatisfactory conduits for cryogenic fluids, the requirement for numerouscentering supports in the vacuum space has added greatly to the cost andcomplexity of manufacture and has penalized the performance of theinsulation. However in the present invention the composite insulationmay serve as the sole centering support for the concentric tubesthroughout the entire hose length between end connections.

Finally the flexible insulated conduit of this invention benefitsgreatly from the relatively moderate vacuum requirement inherent in thehighly effective, alternate layer insulation. The fine fibers obstructheat transport by molecular motion of the residual gas and provide goodinsulation performance with absolute pressures to 100 fold higher thanthose required in systems employing straight-vacuum without filler. Thisis an important advantage in cryogenic hoses where extreme vacuums areexceptionally difficult to maintain because of the repetitivetemperature cycling imposed on the unit.

The following Table I lists suitable specifications for various sizeflexible hoses, constructed in accordance with this invention:

TAB LE I In Table I, nominal I.D. refers to the minimum internaldiameter of a stainless steel tube covered with wire braid, and thecomposite insulation consists of alternate layers of permanentlyprecornpacted glass fibrous unbonded paper and aluminum shields. Thefibrous papers weighed less than 3 grams per sq. ft. and were composedof individual fibers having diameters between 0.2 and 0.5 micron, andlengths of below about 0.5 inch. Also, the aluminum shields were about.0062 mm. thick with an emissivity of about .058. Finally, theinsulation was assembled with a tightness equivalent to about 62 layersof glass fibrous papers per inch thickness. As few as nine layers ofinsulation have been used successfully, that is, with barely discerniblecoolness of the vacuum jacket during a liquid hydrogen transfer.

The corrugated tubing used in the present flexible hose may be purchasedas standard commercial items, and the sizes given in the preceding TableI are determined largely by the dimensions of standard tubes availableon the market. In selecting tube sizes for a given assembly, the minordiameter of the jacket should be sufliciently larger than the majordiameter of the inner conduit to provide ample straight-throughclearance for the insulation.

The insulation space is preferably completely filled with the compositeinsulation to minimize eccentricity between the inner and outer tubesand to maintain contiguous supporting contact between the componentlayers. The total number of insulation layers installed with thereforedepend upon the annular space provided between the tube walls.Preferably the straight'through clearance for insulation should be atleast 0.1 inch and not more than about 0.6 inch. Clearances narrowerthan this range do not provide the requisite number of shields foreflective radiation impedance. Greater clearances contribute onlymarginal insulating value while increasing considerably the heatcapacitive mass to be cooled-down for service. Greater clearances withattendant heavier conduit also penalize unnecessarily the flexibility,lightness and economy of the hose.

The minimum bending radius listed in the last column of Table I is theminimum radius that can be imposed without danger of damage to the hose.These limits are always imposed on corrugated metal tubing regardless ofits use, and normally no precautions are taken to prevent abuse of thehose by bending to a smaller radius. To some extent the wire braid willhelp to restrain the hose from bending beyond the allowable limit. Inthe present hose assembly, the minimum radius is usually imposed by thelarger diameter jacket.

Since it is necessary to maintain the annular space between the twoconduits 1t] and 11 under a substantial degree of vacuum for highinsulating efliciency, a preferred embodiment includes means forremoving gases accumulating in such space. More specifically, anadsorbent such as crystalline zeolitic molecular sieve material havingpores of about 5 angstrom units in size, may be provided for removingtraces of water and air, in accordance with the teachings of U.S. PatentNo. 2,900,800 to P. Loveday. Alternatively, or in addition to theadsorbent, a hydrogen selective getter such as palladium oxide or silverexchanged zeolite X may be provided for removing hydrogen evolved fromthe surrounding metal surfaces in ac cordance with U.S. Ser. No.836,968, filed Aug. 3l, 1959, in the name of L. C. Matsch et al., nowPatent No. 3,108,706.

Some services for cryogenic hoses require intermittent or cyclicoperation in which the cold service periods may be of insufficientduration for eflective use of an adsorbent. In such cases, an activemetal getter such as barium may preferably be employed to remove allresidual gases with exception of the inerts, in accordance with U.S.Ser. No. 792,250 filed Jan. 27, 1959, in the name of A. W. Francis, nowPatent. No. 3,114,469.

The aforementioned adsorbent-getter systems are illustrated in FIG. 3,and rigid tube 17 is provided at least at one end of the flexible hoseassembly. Tube 17 has about the same diameter as corrugated jacket 11,and is bonded thereto at one end. The annulus at the other end of tube17 is sealed to retain the adsorbent by means of a porous plug 18, whichfor example may be formed of glass wool. The end of corrugated innerconduit 10 is metal-bonded to inner, rigid end conduit 19, and the outerend thereof is surrounded by thin-walled, tubular connector 20 having aninner diameter slightly larger than the outer diameter of inner endconduit 19. One end of tubular connector 20 is flared and joined to tube17, and the other end is sealed to the extremity of inner end conduit19.

An annular space 21 is provided between the inner wall of rigid tube 17and the outer wall of inner end conduit 19, and is bounded at one end byplug 18. Composite insulation 13 extends into space 21 to contact plug18. The remaining portion of annular space 21 is filled with anadsorbent, preferably calcium zeolite A as disclosed and claimed in USPatent No. 2,882,243, to remove traces of air and Water accumulating inthe insulation space 12. Other suitable adsorbents include silica geland charcoal. It is to be noted that the adsorbent 22 is locatedadjacent to the cold inner end conduit 19 as its capacity is higher atlow temperatures. An alternate method of installing the adsorbentmaterial is to distribute it sparsely along the length of the flexible,corrugated inner conduit 12 while applying the first layer of compositeinsulation 13. Thus, the adsorbent material 22 is provided incommunicating relationship with the annular insulation space 12.

A sealed capsule 23 formed of glass or other frangible material, andcontaining a suitable amount of active selective hydrogen gettermaterial 24 preferably in a vacuum, is suitably disposed in a getterchamber or protuberance 25 which communicates with the annular adsorbentspace 21. At the desired time, preferably after the space 21 and thecommunicating insulating space 12 have been exhausted by a vacuum pumpor other suitable apparatus, the selective hydrogen getter chamber 25 issuitably deformed as with a pair of pliers or a screw clamp, therebycrushing the glass capsule 23 and exposing the hydrogen selective,active getter material 24 to the communicating spaces 12 and 21. Thecapsule 23 and chamber 25 are preferably held in thermal contact Withthe warm wall of rigid tube 17 since the rate of gettering decreaseswith a reduction in temperature. Palladium oxide is the preferredselective hydrogen getter, although copper oxide and metal exchangedzeolitic molecular sieves such as silver exchanged zeolite X are alsosuitable.

As previously mentioned, adsorbents must be maintained at relatively lowtemperatures to achieve high adsorptive capacities. If the presentflexible hose is to be used under circumstances such that the coldservice periods are infrequent or intermittent, it is preferred toemploy an active elemental metal getter such as finely divided barium.Elemental metal getters remove traces of all predominant gases includingmoisture, air and hydrogen, and their gettering capacities are not assensitive to temperature as are the previously discussed adsorbents. Theactive elemental gettering material may for example be used in sealedcapsule 23 instead of the hydrogen selective getter. In this event,space 21 could be eliminated or alternatively filled with the compositeinsulation 13.

The present invention also includes a method of applying flexible,composite insulating material to a curved surface, the compositeinsulation consisting of a multiplicity of radiation impervious barrierssuch as aluminum foil, and low heat conductive fibrous layers such assheets of glass fiber paper or mats. The installation of such compositeinsulating material presents serious problems since the components arethin, rather fragile and do not conform readily to a compound curvature.For example, it has been found that if the insulation is applied assmooth continuous tubes of foil and fiber, even moderate flexing causesthe foils to shorten and draw back from the hose ends as a result ofwrinkling and buckling. This exposes a considerable length of the innerconduit to radiation. More severe flexing of continuous foil layerscauses the foils to break or tear, thereby producing windows for radiantheat flow. These problems are overcome by providing the radiationimpervious barriers in elongated strips. As illustrated in FIG. 4, theradiation-impervious strips are helically wrapped without bonding aroundthe curved surface, e.g. cylinder 31, from one end to the other endthereof so as to provide an overlap between adjacent edges 32 and 33 ofadjacent helices, e.g. 34 and 35.

The overlapped edges of the helical windings slide one upon the other asthe hose is flexed and this eliminates the foil-shortening problemencountered with continuous foil layers. The degree of overlap isimportant and must be sufficient to prevent spreading the edges of thewindings apart when the hose is flexed to the minimum radius expected inservice. Spreading the windings should be avoided since this opensunshielded areas in the insulation and increases radiation. Furthermorethe separated edges will catch one on the other when the hose is againstraightened thus wrinking or tearing the ribbon edges and producingpermanent radiation Windows. An overlap of 18% of the strip Width isconsidered the minimum for dependable insulation performance, while anoverlap in excess of 30% is unnecessary and should be avoided since itadds excessive heat capacitive material and increases cool-down losses.An overlap width of about 20% of the radiation impervious strip widthrepresents a preferred balance between heat capacitive mass anddependable insulation performance.

When the curved surface is cylindrical as for example the presentflexible hose, it has been found that the radiation impervious stripshould have a width between and of the cylinder diameter. This range isadvantageous because the resultant insulation is economically applied,and in the case of the hose, the insulation will possess a flexibilitywhich is approximately matched to the flexibility of the hose.

On completion of helical wrapping the curved surface from end-to-end, afirst radiation-impervious barrier is formed. As illustrated in FIG. 5,a concentric layer 36 of the low heat conductive fibrous material isthen applied around the outer surface of the helically wound firstradiation impervious barrier so as to completely cover the barrier. Thefibrous material layer can, for example, be applied satisfactorily byhelical wrapping or as individual sheets of any convenient length, thewidths of which are at least as great as and preferably equal to thcircumference of the layer being applied. A second, helically woundradiation-impervious barrier is then formed around the outer surface ofthe concentric layer of the low heat conductive fibrous material in thesame manner as the first radiation impervious barrier so as tocompletely cover the low conductive fibrous layer. Thereafter,additional layers of low heat conductive fibrous material and barriersof radiation impervious material are similarly applied in alternatingsequence and in sufficient quantity to achieve desired degree of thermalinsulation for the curved surace.

As mentioned above, the low-conductive fibrous component of theinsulation may also be applied in the form of strips wound helically toform discrete layers separating the layers of radiation barrier. Whenthe fibrous component is used in strip form, still another mode ofapplying the composite insulation in concentric layers is possible. Theradiation barrier and fiber strip materials may first be overlaid andthen wound on the conduit as though a single strip. The appearance ofthis construction is shown in FIG. 6 with the thickness of insulationlayers greatly exaggerated for clarity. To avoid contact betweenradiation barriers in adjacent layers, the fiber strip should be widerthan the radiation barrier, and the two strips should be overlaid withmarginal fiber material extending beyond both edges of the radiationbarrier. As illustrated, flexible corrugated inner conduit 11 issurrounded by wire braid 14;, and three composite insulation layers 40,41 and 42 of pregressively increasing diameters. Each layer comprises astrip 43 of low-conductive fibrous material and a relatively narrowerstrip 44 of radiation impervious material.

Viewed in cross-section, a curved surface insulated by the presentwrapping method using any of the described techniques results indiscrete concentric cylinders of insulation components. The radiationbarriers are entirely separate one from another without metalliccontact.

In an alternative method of applying this composite insulation, asdisclosed for example in previously referation of the shield around theinsulation layer. While this.

continuous spiral technique is satisfactory for insulating largeconduits or tanks, it is not the preferred method for small size objectssuch as the conduits of this invention. This is because the heatconduction inward along the spiral shield is suflicient to reducesignificantly the temperature difference between layers and thus disturbthe temperature gradient through the insulation thickness. For example,in a 3-inch diameter layer heat transmission through the insulation istheoretically increased more than when spiral, rather than concentricshields are used, while in 2-inch and 1-inch layer sizes the increase ismore than and 170%, respectively. Furthermore, it is difficult to employthe overlapping ribbon technique to achieve flexibility when using thecontinuous spiral method of insulation. For the above reasons, thecomposite insulation is preferably applied as concentric layers in oneof the previously described modes.

This composite insulation assembly method employing concentric layers isparticularly suitable for applying the insulation in annular space 12between the flexible inner conduit 10 and outer jacket 11 of theflexible hose assembly of this invention. Also the radiation imperviousbarriers of such assembly method are preferably helically Wound metallicribbon having a thickness between about 0.002 and 0.2 mm. and a widthbetween 125% and 185% of the conduit diameter. The low heat conductivefibrous component is preferably a permanently precompacted paper, andthe composite insulation is applied with sufficient tightness to providebetween 40 and 250 shields per inch of thickness, under a compression ofless than 0.03 lb. per square inch. Alternatively, the low heatconductive fibrous component may be a relatively loose web of fiberswhich is preferably compressed sufliciently during installation toprovide between about 5 and radiation shields per inch of insulationthickness.

Although preferred embodiments have been described in detail it will beunderstood that modifications and variations may be efiected withoutdeparting from the spirit and scope of the invention.

Whit is claimed is:

1. A method for applying flexible, composite heat insulating material tothe outer curved surface of a cylindrical conduit for transporting lowtemperature liquids, the composite insulation consisting of amultiplicity of radiation impervious metallic strips of thicknessbetween about 0.002 and 0.2 mm. and low heat conductive fibrous layers,which method comprises the steps of providing said radiation-imperviousmetallic strips and low heat conductive fibrous layers in elongatedoverlaid strips with marginal fibrous material extending beyond bothedges of each radiation-impervious metallic strip to form a compositestrip; helically wrapping said composite strip around said curvedsurface from one end to the other end thereof so as to provide anoverlap between adjacent edges of adjacent helices and thereby form acomposite insulation layer; forming a second helically Wound compositeinsulation layer around the outer surface of the first in the samemanner so as to completely cover the first composite insulation layer;thereafter similarly applying additional layers of composite insulationin sufiicient quantity to achieve a desired degree of thermal insulationfor said curved surface.

2. A method according to claim 1 wherein said curved surface is theouter side of a flexible corrugated metallic inner conduit fortransporting low temperature liquids, and the outer surface of saidflexible, composite heat insulating material is contiguously associatedwith the inner surface of a larger flexible corrugated metallic jacketbeing concentrically spaced around the inner conduit.

3. A method according to claim 1 wherein the width of said radiationimpervious strip is between and of the cylinder diameter.

4. A method according to claim 1 wherein said low heat conductivefibrous layers are sufliciently elastically compressed so as to providebetween about 5 and 50 radiation impervious barriers per inch ofcomposite insulation thickness.

5. A method according to claim 1 wherein said low heat conductivefibrous layers are permanently precompacted paper, and the compositeinsulation is applied sufiiciently tightly around said curved surface soas to provide between about 40 and 250 shields per inch of thickness,under a compression of less than 0.03 lb. per sq. in.

6. A method according to claim 1 wherein said metallic strips are formedof aluminum foil.

References Cited UNITED STATES PATENTS 338,733 3/1886 Habirshaw 57-1601,942,468 1/ 1934 Andrews 138111 2,170,207 8/1939 Mosier et al. 138-1292,858,854 11/1958 Daggett. 2,954,803 10/1960 Barnes et al. 138-1433,136,113 6/1964 Cullen et al. 57-160 CHARLIE T. MOON, Primary Examiner.

1. A METHOD FOR APPLYING FLEXIBLE, COMPOSITE HEAT INSULATING MATERIAL TOTHE OUTER CURVED SURFACE OF A CYLINDRICAL CONDUIT FOR TRANSPORTING LOWTEMPERATURE LIQUIDS, THE COMPOSITE INSULATION CONSISTING OF AMULTIPLICITY OF RADIATION IMPERVIOUS METALLIC STRIPS OF THICKNESSBETWEEN ABOUT 0.002 AND 0.2 MM. AND LOW HEAT CONDUCTIVE FIBROUS LAYERSWHICH METHOD COMPRISES THE STEPS OF PROVIDING SAID RADIATION-IMPERVIOUSMETALLIC STRIPS AND LOW HEAT CONDUCTIVE FIBROUS LAYERS IN ELONGATEDOVERLAID STRIPS WITH MARGINAL FIBROUS MATERIAL EXTENDING BEYOND BOTHEDGES OF EACH RADIATION-IMPERVIOUS METALLIC STRIP TO FORM A COMPOSITESTRIP; HELICALLY WRAPPING SAID COMPOSITE STRIP AROUND SAID CURVEDSURFACE FROM ONE END TO THE OTHER END THEREOF SO AS TO PROVIDE ANOVERLAP BETWEEN ADJACENT EDGES OF ADJACENT HELICES AND THEREBY FORM ACOMPOSITE INSULATION LAYER; FORMING A SECOND HELICALLY WOUND COMPOSITEINSULATION LAYER AROUND THE OUTER SURFACE OF THE FIRST IN THE SAMEMANNER SO AS TO COMPLETELY COVER THE FIRST COMPOSITE INSULATION LAYER;THEREAFTER SIMILARLY APPLYING ADDITIONAL LAYERS OF COMPOSITE INSULATIONIN SUFFICIENT QUANTITY TO ACHIEVE A DESIRED DEGREE OF THERMAL INSULATIONFOR SAID CURVED SURFACE.